1. Field of the Invention
The present invention relates to a method of and a device for preparing an existing underground or buried main or conduit for replacement by a new main by means of a mole device that is moved through the existing main, with the new main clamped or otherwise secured to the mole device. The mole device fractures the existing main from within by compressive and impact forces, and widens the bore thereby created for the insertion of the new main.
2. Description of the Prior Art
U.S. Pat. No. 4,505,302 Streatfield et al dated Mar. 19, 1985 discloses a method of replacing an existing buried main, without excavation, with a new main having a diameter which is equal to or greater than the external diameter of the existing main. According to this method, the existing main is fractured from within by a mole device that is moved through the existing main, with sufficient clearance being provided through the fractured main for movement therethrough of a new main that is clamped to the mole device. According to this U.S. patent, the method is suitable for and applicable to cast iron mains sufficiently brittle, as is generally known, for fracturing by a hammer blow or the like. In other applications, though, buried mains of a tough or ductile material such as steel or plastic must be replaced by new mains of the same or a larger diameter which cannot therefore be inserted into the existing main. The method proposed by said U.S. patent has been unsuitable for mains consisting of pipes of such material.